1. Field of the Invention
This invention relates to a copying apparatus which is capable of selectively effecting one-side printing and both-side printing, as required.
2. Description of the Prior Art
Copying machines of the prior art have generally been of the single-side printing type which are capable of printing only one side of a copy medium. According to such prior art systems, the quantity of copies produced is double the quantity of copies which would be produced by a both-side printing system, and where huge quantities of copies are to be stored, this has been disadvantageous in terms of storage space, weight and cost.
Some types of image transfer copiers capable of both-side printing have heretofore been conceivable. A first one of them is the type which uses two photosensitive drums to form thereon discrete images which are to be transferred to the opposite sides of a copy medium. This is simple in principle but requires two sets of copying process elements which in turn leads to a higher cost and larger scale of the apparatus. A second type uses a single photosensitive drum and a mediate drum in such a manner that an image to be transferred to one side of a copy medium is first formed on the photosensitive drum and transferred to the mediate drum for temporary preservation thereon, whereafter an image to be transferred to the other side of the copy medium is formed again on the photosensitive drum, and then the two images are transferred from the mediate drum and the photosensitive drum to the opposite sides of the copy medium, respectively. This second type involves only one set of copying process elements but requires the image transfer to be effected twice through the agency of the mediate drum, thus resulting in a reduced image transfer efficiency and other disadvantages.